Method and device for the molding of wood fiber board

ABSTRACT

The invention relates to a method and device with which it is possible to arrange complicated shapes with considerable differences in height in wood fibre board, and in particular but not exclusively so-called MDF (Medium Density Fibreboard). The deformation of the wood fibre board which can be achieved with the invention is known in the art as extrusion, wherein a considerable plastic deformation takes place accompanied by flow and stretch of the material.

This application is a Division of Ser. No. 09/402,603 filed Dec. 21,1999 U.S. Pat. No. 6,500,372 which is a 371 of PCT/NL98/00233 filed Apr.27, 1998.

The invention relates to a method and device which can be used toarrange in wood fibre board, and in particular but not exclusively inso-called MDF (Medium Density Fibreboard) complicated shapes withconsiderable differences in height. The deformation of wood fibre boardwhich can be achieved with the invention is known as extrusion, wherebyconsiderable plastic deformation, accompanied by flow and stretch of thematerial takes place.

The deformation of wood fibre board is known as such. From theInternational patent application WO96/03262 for instance a method isknown with which it is possible to bend wood fibre board to a bendingradius of minimally 2.5 times the thickness of the board material.

From other publications, such as for instance the European patentapplication 0 420 831 it is known to provide wood fibre board with asurface profiling by subjecting this material to a pressing operation.In this case the required profile is formed by locally varyingcompression of the material.

The deformation which can be effected with the invention can be muchmore comprehensive than the deformation which is achievable with thestate-of-the-art methods.

The invention will be explained in greater detail in the followingdescription with reference to the attached drawings.

FIG. 1 illustrates schematically a device according to a preferredembodiment of the invention.

FIG. 2 illustrates a door skin manufactured with the device and methodaccording to the invention.

FIG. 3 shows a detail of the section as indicated by arrow II in FIG. 2.

FIG. 4 shows a cross-section of the door skin of FIG. 3 along the lineindicated by arrows IV—IV, together with the corresponding mould parts.

FIG. 5 shows a view corresponding to figure of another embodiment.

FIG. 6 shows a cut away perspective view of another embodiment of a doorskin.

FIG. 7 shows an example of a pressing cycle employed with the methodaccording to the invention.

FIG. 8 shows a detail of a pressing cycle.

FIG. 9 shows partly perspective views of a front side and correspondingback side of a door skin manufactured with the method according to theinvention according to a preferred embodiment.

FIG. 10 shows a partly broken away perspective view of an embodiment ofthe press according to the device of the invention as indicated by arrowX in FIG. 1.

FIG. 11 shows a perspective view of the section as indicated by arrow XIin FIG. 1.

FIG. 12 shows the press of the device according to the invention in theclosed state, prior to changing the moulds.

FIG. 13 shows a detailed view of the section indicated by arrow XIII inFIG. 12.

FIG. 14 shows a view corresponding to the one of FIG. 13 during anotherphase of the action of the changing means.

FIG. 15 shows a view corresponding to that of FIG. 12 during anotherphase of the action of the changing means.

FIG. 16 shows the carrier frame of FIG. 15.

In general, the device 1 as illustrated in FIG. 1 comprises a conveyor 4on which wood fibre boards, in particular MDF boards are conveyed. Theconveyor 4 takes boards 2 into a chamber 16 of a forming station 5. Inthis chamber 16 the boards 2 are heated in a manner to be describedbelow in detail and treated with steam in such a way that the materialreaches it thermal softening point.

In this softened state the boards are taken from the forming station 5into the forming area 8 of a press 7. This is done with a conveyor 6.

In the press 7 the forming area 8 is bounded at the top and bottom by anupper mould 9 and a lower mould 10 respectively which delimit in theclosed state of the press a specifically shaped mould cavity which willbe described in greater detail below.

Next the press 7 is activated as a result of which the upper mould 9 ismoved in the direction of the lower mould 10, whilst the thermallysoftened wood fibre board is positioned in between.

By a carefully defined course of movement of the upper mould 9 to bedescribed in greater detail below, the wood fibre board will beconsiderably plastically deformed as a result of which a complicatedprofile can be arranged in it. With the example of the embodiment showntwo wood fibre boards can be processed simultaneously, in whichaltogether six door skins will be formed, i.e. three door skins per woodfibre board 2.

In the mould parts 8,9 knives have been formed at the edges in betweenthe separate door skins which cut grooves 11 in the boards at the edgesof the door skins along which the boards can be broken easily.

The lower and upper mould 10, 9 which can, as explained above, form inthis embodiment six door skins placed next to one another, havepreferably been made up of six separate upper and lower mould parts, onefor each door skin to be formed. The specific embodiment of the doorskins to be manufactured can thus be altered per mould part, so that theproduction may be adapted to the demand for specific models.

Before the boards 2 are moved into the forming area 8 of the press bymeans of the conveyor 6, a sheet of plastic may be arranged on top of itwhich may be joined during the pressing operation with the top surfacesof the boards 2. A very suitable material for this purpose is melaminepaper. The ultimate product will in that case obtain a synthetic surfacewhich is desirable for certain applications. Additional finishingoperations to the objects produced, such as the door skins 3, areconsequently no longer necessary.

The method and device according to the invention have been describedabove in very general terms. The different sections will be explainedbelow in greater detail.

An important aspect of the method according to the invention is thechoice of the basic material. Both where the wood fibre material, and ifapplied, the melamine paper are concerned.

It has become apparent that where the choice of wood fibre material isconcerned the maximum thermal softening which can be attained and thetemperature at which this is achieved are decisive. The thermalsoftening point is a function of the wood species and the chemicalproperties of the board material. Also important are the cellularmoisture content and the quantity of heat supplied. Softening at as lowas possible a temperature is favourable.

The selection of a favourable basic material can be made experimentallyby establishing for a test piece the thermal softening point and thedegree of thermal softening at that point. It has become apparent thatmaterial made of a wood fibre with long fibres is favourable. Inparticular pine is very suitable to be used as basic material.Preferably radiata pine is used, for which the thermal softening alreadystarts at 95° C.

For the melamine employed a type of paper is chosen which reacts slowly,as opposed to the fast reaction which is normally required forlamination purposes et cetera. The curing time should be longer than 10seconds and preferably be something like 20 seconds. Thus it is possiblethat the curing of the melamine only takes place after the wood fibreboard has been deformed maximally.

In order to be able to take up the required strong deformation,preferably a material with a carrier of shrunk i.e. crepe paper is used.

The treatment during which the board material acquires the softenedstate takes place in the forming station 5. The chamber 16, inside ofthe which the boards 2 to be treated are received, can be closed offhermetically. In the forming station 5 vacuum pumps which have not beenillustrated have been arranged, which create a partial vacuum inside thechamber 16 as soon as the boards 2 have been received in the chamber 16and the latter has been closed. When a suitable underpressure has beenreached, steam from a boiler 15 is introduced into the chamber 16. Dueto the steam supplied the pressure inside the chamber 16 will rise againto roughly atmospheric pressure and at the same time the steam will alsoquickly penetrate the pores of the wood fibre board 2.

The steam exhaust in the chamber 16 consists of a number of nozzlesarranged in the bottom of the chamber pointing upwards, which squirt thesteam supplied like a jet against the underside of the board 2. As aresult and together with the sucking action due to relieving theunderpressure, penetration of the steam is achieved.

In the boiler 15 the steam is generated under an overpressure of severalbars, preferably more than 10 bars. Due to the expansion in the chamber16 the temperature of the steam will drop to just above 100° C. andimmediately some of the steam will condensate inside the board. Theboard is both heated and moistened.

In addition to being heated due to direct contact with the steam, theboards 2 inside the forming station 5 are heated due to the fact thatthe walls of the chamber 16 themselves are heated and give out heat tothe boards 2 received in the chamber 16 by means of radiation. In theexample of the embodiment illustrated here, the cover 17 of the chamber16, which may be a lid, is hollow and has been connected to the steamsupply. The cover of the chamber 16 will as a result obtain a hightemperature corresponding to that of the steam inside the boiler 15,which temperature is consequently higher than that of the expanded steaminside the chamber 16.

Because of this high temperature of the cover of the chamber 16, properheating of the board 2 by means of radiation will take place, whilst itis also prevented that the expanded steam will condense against thiscover. It has been found that drops of water on the boards 2 will resultin serious defects in the final product. By heating the cover of thechamber 16 until it has substantially the same temperature as the steamused for expansion, condensation is prevented.

The generated steam has consequently two functions. In the state with ahigher pressure and temperature it serves for heating the walls of thechamber 16 and in particular the cover thereof and in the expanded stateinside the chamber 16, when the temperature and the pressure are lowerdue to the expansion, it serves for moistening and heating the boards 2.

The greater the underpressure in the chamber 16 prior to the supply ofsteam, the shorter the duration of the treatment of the boards. It hasbeen established that at the pressure of 0.8 bar mentioned, the durationof the treatment of wood fibre boards of the radiata pine referred toabove, will be 15 to 30 seconds. This is already considerably shorterthan the pressing cycle time of the press 7, so that the duration of thetreatment in the forming station 5 is not decisive for the productioncycle.

With other kinds of wood a greater underpressure may be required inorder to attain the required short duration of the treatment after all,so that it does not affect the cycle time of the production. Theduration of the treatment of MDF board of wood fibres of the rubber tree(haevea brazilienzis) takes at an underpressure of 0.8 bar four timeslonger as, when using that material, such a low underpressure is notsufficient. The underpressure will have to be greater in order toachieve a suitably short treatment time.

By way of compensation for the loss of heat during the followingtransport phase, the wood fibre material in the forming station 5 isheated as much as possible, but not so high that it would become tooweak to be handled when it has to be positioned inside the press.

In practice it has been found that a temperature of about 100° C. is themost suitable for an MDF board with a thickness of 3.8 mm made of theradiata pine wood fibre mentioned above.

When the wood fibre boards 2 have been pre-treated in this manner, theyare subjected to the real extrusion treatment in the press 7.

To achieve maximum deformation during the extrusion treatment, carefulcontrol of the pressing cycle and a specific design of the mould cavityare important in addition to the choice of the basic material and thesoftening.

This last aspect will be explained in greater detail with reference toan example of a product to be manufactured with the method and deviceaccording to the invention, that is to say the door skin 3 mentionedabove, as illustrated in greater detail in FIG. 2.

FIG. 2 shows at 20, 21 and 22 the front side, the back side and thebasic material respectively of a door skin 3 manufactured with themethod and device according to the invention. Such a door skin 3 will bearranged on a wooden framework in a manner known as such, whereby asimilar or other door skin 3 will be arranged to the other side of thisframework. The assembly thus formed forms a door which has theappearance of a door made up of posts 24, cross pieces 25 and receivedin between those, panels 26. This appearance is obtained by extrudingprofiles 23 in a board of basic material 22 in the manner indicated.

It will be clear that the total surface area of the door skin 3 islarger than that of the board of basic material 22. In order to form theprofiles 23 material of the board is moved from adjoining sections intothis profile.

FIG. 3 shows a detail of the section indicated by arrow III in FIG. 2,in which the arrows 26, 27 indicate the movement of the material in thedirection of the profile 23 during extrusion. It will be clear thatespecially in the cross in which the arrows 27 have been drawn aparticularly critical situation arises as regards the strain put on thematerial of the board during extrusion. The forced movement of thematerial could lead to tearing, or in less serious cases to debonding offibres at the surface.

With the method and device according to the invention it is possible tosubject wood fibre material to such extrusion treatment which puts thematerial under tremendous strain.

An important measure of the invention is controlling the movement of thematerial during extrusion. By means of measures to the moulds to beexplained in greater detail below, it is ensured that the direction fromwhich the material during extrusion flows towards the profile iscontrolled, so that it is for instance prevented that too much materialfrom the central section of the cross illustrated in FIG. 3 flows to theprofiles in the direction indicated by the arrows 27, as a result ofwhich the damage to the material as mentioned above could occur.

This effect is achieved because the mould cavity comprises in the closedstate of the mould local constrictions which grip the board material,and retain it before the complete deformation has taken place. The flowof material via this narrowed section is consequently counteracted. InFIG. 4 an upper mould 9 and a lower mould 10 have been illustrated at acertain distance from one another with a just moulded door skin 3 inbetween. The shape of the door skin 3 corresponds to the shape of themould cavity in the closed state of the upper and lower mould 9, 10. Thesection illustrated in FIG. 4 concerns the section in which part of theprofile 23 is formed. The local constrictions of the mould cavity havebeen indicated with the arrowheads 31, 32 and 33. For the deformation ofan MDF board of for instance 3.8 mm, the general height of the mouldspace indicated with the number 30 will be roughly 3.2 mm. This meansthat also in those sections which are not extruded directly there willbe a compression of material.

At the narrowed sections 31 and 32 the mould height is for instanceroughly 2.7 mm. At 33 the height of the mould cavity is once again 3.2mm.

It will be clear that when closing the mould first, a gradual stretchand flow of the material from all directions will take place in theprofile 23. With the last (3.8−2.7=) 1.1 mm of the stroke of the pressthe board is already retained at the constrictions 31 and 32. During thelast part of the stroke, when the details of the profile are beingformed, and when locally the greatest strain on the material may beexperienced, there will be no more flow into the profile 23 from theright. Also the area in between the arrows 31 and 32 is enclosed and nomore movement of material can take place there. The movement of materialstill required for the formation of the bottom section of the profilewill come from the left. As the left side of the profile has lessdetails, material strain during flow from that direction will remainlimited.

Because of these local constrictions 31 and 32 it is consequentlyprevented that during the last stage of the formation of the profile,material form the right is being pulled into the profile as a result ofwhich too great a material strain at the right hand side of the profilecould occur, resulting in tearing and debonding of fibres at the surfaceof the board 3.

A further important measure is that the mould parts 9 and 10 have beenheated, and that consequently, due to contact with the board 3, thisboard is heated even further. In the narrowest sections of the mouldcavity, in this embodiment at the arrows 31 and 32 the first narrowcontact between the mould parts 9 and 10 and the board takes place, as aresult of which these areas are heated first and the most. Theplasticity of the board increases due to the increase in temperature,which contributes to the required flow of the material during theextrusion.

An additional effect of the constrictions in the cavity of the mould isthat fibres which may have become debonded after all, are pressed undergreat pressure into the surface of the board. The suitable wood fibreboards such as MDF boards comprise a binding agent which usually is notfully hardened yet. Due to the strong pressure and the heating, furtherhardening of this binding agent will take place, whereby in the statefollowing extrusion the wood fibres will be bonded well. Fibres whichmay have become debonded at the surface following movement of materialare bonded once again firmly to the material in this manner.

In FIG. 5 a section of an upper mould 35 and a lower mould 36 are shownwith a section of a board 37 just formed in between. In the case of thisembodiment the profile 38 is somewhat simpler than the profile 23 ofFIG. 4. As a result one narrowed section will suffice, which has beenindicated with the arrowheads 39 at the right hand side of the profile,with which it is prevented that following the initial deformation morematerial will flow from the right into the mould cavity forming theprofile.

Although with the example of the embodiment shown the shape of the mouldcavity is essentially everywhere the same, in certain cases the localconstrictions of the mould cavity may vary along the length of theprofile. It will be clear that for instance the movement of materialwill be the most critical at an corner in the profile, and thatconsequently the control of the movement of material needs to beproperly managed. At other locations along the profile less stringentrequirements as regards this control may apply.

As has already been illustrated in the example of FIG. 6, showing asection of an extruded board 40, the risk of damage to the material as aresult of too much strain applied to the material due to uncontrolledmovement of material will be greatest at the corner 42 in between theprofile part 41 and the profile part 43. It goes without saying thatclose to this section 42 the movement of material during extrusion willhave to be controlled by local constrictions in the mould cavity.

As has been illustrated with the embodiment, the local constrictions maybe formed by giving the walls of the cooperating mould parts a suitable,fixed shape. It is also possible however to control the movement ofmaterial by means of movable elements received in the mould, which at acertain distance of the upper and lower mould retain the board to beextruded in a required manner, so that at that site no more movement ofmaterial can take place during extrusion. These movable sections may forinstance be formed by steel sliding pieces but also insert pieces madeof a rubber-like material are feasible.

The position of the local constrictions or the movable mould partsobviously depends on the shape to be extruded. When designing this shapeit should often already be possible to determine where the most criticalsections are located and determine based on that where the board to beextruded has to be retained in order to control the flow of material.When, during the first trial pressings, it becomes apparent that damagedue to incorrect movements of material occurs in certain areas, themould can be adjusted accordingly. Considering the above, theseadjustments will be obvious for an expert in the field.

Besides the measures described above already which enable extrusion of awood fibre board with a very complicated shape, measures as regards thepressing cycle are possible as well.

FIG. 7 shows schematically a suitable pressing cycle as employed withthe method according to the invention. On the horizontal axis time isplotted in seconds and on the vertical axis the moulding pressure inkg/cm² and at the same time the distance between the mould parts inmillimetres. The dotted line indicates the distance between the mouldparts whilst the continuous line indicates the pressure.

The cycle begins when the softened wood fibre boards have beenpositioned inside the mould. At that moment the press will close veryrapidly until both parts of the mould just make contact with the board.Next the mould closes very slowly until it is closed completely. Whenthe mould is closed completely the pressure is built up and maintainedfor a certain period of time, after which the pressure falls topractically zero and is built up again after some time. This is repeatedonce again for reasons which will be explained below. When the pressurehas fallen to zero for the third time the mould is opened and theproduct will be ready to be removed from the mould.

The mould closes rapidly during the first part of the closing cycle inorder to achieve as short as possible a cycle time. The second part ofthe closing cycle is however crucial to proper extrusion treatment.

An example of the closing cycle during this second part has beenillustrated in greater detail in FIG. 8. The first step has in this casebeen indicated with the reference number 50. This is the step duringwhich the mould closes rapidly. At the end of this step the mould partsjust make contact with the board. The speed is then greatly reducedduring step 51 in order to effect a gradual movement of material to formthe rough shape of the profile. Then the speed is reduced further duringstep 52 and during step 53 the movement is stopped all together. Strainsbuilt up in the material may now be equalized and at the same timeheating of the board will take place due to contact with the heatedmould parts, as a result of which the deformability of the material ofthe board increases again. Next, the mould closes again a degree furtherduring step 54 and the movement is stopped again during the followingstep 55. Also during this step the material strains which have built upcan be equalized again and the material can flow and stretch. The lastpart of the closing cycle, during the step 56, takes place graduallyagain. Then the mould is closed and the pressure is built up.

The course of the graph described here depends on the profile formed. Ingeneral the closing speed will be minimal or even zero when the mostcrucial parts of the profile are being formed. A closing speed which istoo high during the moulding phase concerned will be detectable in thefinal product because material defects, mainly visible at the surface,will occur. These material defects may for instance be loose fibres oruneven surface sections. Based on the final results the expert will beable to ascertain whether in a certain moulding phase the closing speedwas too high or whether it could still be a bit higher. Thus theappropriate closing curve can be established experimentally, premisebeing that the speed should be low or at least almost zero when thedeformation caused by the activated mould involves maximal materialstrain. In addition there should always be sufficient time for heattransfer from the mould parts to certain sections of the material whichare about to be deformed significantly.

As has been said before and as can be seen in FIG. 7, the pressure isbuilt up following this specific closing cycle. In FIG. 7 the maximumpressure is just over 60 kg/cm², but in many cases a lower pressure willsuffice like for instance ±40 kg/cm². The required compression of thematerial in the case of the example described above of a board with aninitial thickness of 3.8 mm to 3.2 mm can then be achieved. In that casethe entire board is heated to more or less the temperature of the mouldparts, which will for instance be about 200° C. After some time thepressure will be reduced to almost zero. It should be noted that thedistance between the mould parts does not alter.

Due to the pressure decrease, the water in the board material, which hasbeen heated well beyond the atmospheric boiling point, will suddenlybecome steam and this steam will escape sideways between the moulds.Next the pressure is increased again to the maximum value employed andkept at this level for some time, whereby the still remaining water isheated again. Most of this water will escape once again the next timethe pressure is reduced to zero, after which for a last time thepressure is increased to the maximum value employed and maintained atthis level for some time. After the mould has been opened, the moisturecontent of the wood fibre material has fallen to a very low value ofabout 5%.

The drying and degassing cycle described here takes place whilst themould parts remain in close contact with both sides of the boardmaterial. It is thus prevented that due to the expansion of the water,the wood fibre material would be pushed apart which could lead tosurface defects of the product. Because the pressure does decrease butthe mould parts do not move in relation to one another, the boardremains supported over its entire surface area, as a result of which nomovement of wood fibres due to the water vapour pressure can take place.

Usually 2 to 3 drying-degassing steps will be required, depending on thewater content of the material, the temperature of the mould and otherproperties of the material. The mould temperature can, depending on thematerial, be set at a value of for instance 160-200° C.

The closing cycle described with reference to FIG. 8 can, depending onamong other things the complexity of the profile, last 20 to 30 seconds.During these 20 to 30 seconds the last 6 to 8 mm of the closing distanceare covered in a number of steps.

It will be clear that considering the accuracy with which this movementhas to be carried out, the press will have to comply with the strictestrequirements. These requirements concern both the accuracy with whichthe closing speed of the press can be controlled and the accuracy withwhich the mould parts can be kept parallel in relation to one another.

It must be possible to fully control the closing speed of the press andpreferably also to vary the speed between 0.1 to 50 mm/sec. The highspeed is required to limit the loss of time when initially closing andwhen opening the press so as to enable commercial production.

With a press which is part of the device according to the invention, theaccuracy of the adjustment of the closing speed is 0.1 mm/sec.

Also the pressure is fully adjustable, preferably in steps of 0.5 kg/cm²to a maximum of for instance 65 kg/cm² for the embodiment describedhere.

In order to be able to manufacture the product described here, i.e. thedoor skins, in a commercial manner, moulds for making six door skinsduring one pressing cycle are employed simultaneously. The workingsurface area of the press is consequently of the order of 2.2×5.6 m.Over this relatively large area the deflection is not allowed to begreater than ±0.1 mm at a full moulding pressure, so that in allsections of the mould the required accurate control of the closing speedin relation to the profile can be achieved.

Also the parallelism of the upper and lower mould must meet high valuessuch as ±0.1 mm.

The maximum operating temperature of the sections of the press to whichthe mould parts are attached is about 200° C. The temperature variationover the total working area of the press must remain within ±2° C., inorder to be able to achieve once again, at every section of the moulds,the required accurate conditions. Preferably those sections of the presscarrying the moulds are heated by means of thermal oil. In order toachieve the great accuracy of temperature, conduits have been arrangedalong the entire length of the platens through which this thermal oilflows in a parallel fashion.

It will be clear that when the extrusion process is less complicated therequirements the press has to meet will be less severe.

FIG. 9 shows a partial view at enlarged scale of the section indicatedby arrow IX in FIG. 2. The front side 20 of a manufactured door skin 3and next to it the back side 21 of the same door skin 3 have beenillustrated.

It can be seen that a wood grain pattern has been arranged to the frontside 20. To this end the upper mould has been provided with acomplementary relief. This relief may have been formed in a suitablemanner in the surface of the mould by means of photo etching. The reliefis transferred to the wood fibre board by impressing it into it. Atcertain sections the board will be compressed more, as a result of whichgrooves will be formed which correspond to the lines of the wood grainpattern.

At the back side 21 a pattern 60 has been formed as well. This has alsobeen arranged by means of impressing a relief formed on the lower mould.This relief may also have been arranged by means of photo etching and issuch that the back side 21 of the door skin obtains a certain roughness.Because of this roughness glue will adhere very well to the back side 21of the door skin, so that a door made with the door skin 3 will have along life span without a risk of the door skins coming loose. Thepattern 60 is preferably formed by small set back and protrudingsections, the size of some tens of millimetres. In addition to betteradhesion of the glue due to the roughness, better adhesion is alsoachieved because of area enlargement.

FIG. 10 shows a partly broken away detailed view of the press 7according to a preferred embodiment of the invention. In this figure theupper and lower mould 9 and 10 can be seen in greater detail and alsothe fastening means, still to be described, with which they have beenmounted to the upper platen or press platen of the press 7 and the lowerplaten respectively.

Through the broken away section of the press platen 59, the conduits 60can be seen which have been described above and serve to convey thethermal heating oil.

The loading and unloading of the boards and extruded productsrespectively is carried out by a supply carriage 62 and a dischargecarriage 70 which can move along rails 61 which extend on either side ofthe lower platen over a distance in front of and behind the press 7. Therails 61 are profiles on which wheels arranged to the frames of thecarriages 62,70 can move. The careful cross positioning of the supplycarriage 62 is achieved by means of transverse guides 63.

The supply carriage 62 itself has been provided with a conveyor 64 whichcan consequently be moved along with the carriage 62.

As has been explained before, in this case two boards 2 are taken fromthe forming station 5 on the belt 65 of the supply carriage 62, afterthese boards have been softened in the forming station 5. When leavingthe forming station 5 the supply carriage 62 is positioned as far to theleft as possible, i.e. in front of the press. The boards supplied fromthe forming station 5 are positioned carefully on the belt 65. When thishas been done the entire carriage 62 enters the press without theconveyor 64 moving. As soon as the carriage 62 has reached a position inwhich the boards 2 lying on the belt 65 thereof have taken in theircorrect relative position in relation to the mould, the carriage 62 ismoved back whilst at the same time the conveyor 64 is driven at the samespeed but in the opposite direction. The boards 2 consequently maintaintheir relative position in relation to the mould and are positionedcorrectly in relation to the mould on the lower mould 10. The carriage62 is pulled away as it were from underneath the boards.

After the boards have been positioned on the lower mould and the supplycarriage 62 has been moved back, the pressing cycle described above iscarried out for the purpose of extrusion of the door skin 3.

After the press has been opened again, the door skins 3 formed may betaken from the press area by means of the discharge carriage 70illustrated in FIG. 11. As has been mentioned, this carriage can alsomove along the rails 61. As can be seen in the figure the carriage 70has a U-shaped frame, whereby the legs of this frame can be moved alongthe rails 61. Arm carriers 71 have been arranged to the frame 69. Theseare elongated beams which extend parallel to the legs of the frame 69and can be moved in a vertical direction between a high and a lowposition by means of vertical guides. Movement of these arm carriers 71is effected by means of cylinders 73.

Each time three arms 74 have been arranged to the arm carriers 71. Thesecan turn from the projected position illustrated in FIG. 11 to aposition turned to the right in FIG. 11, in which they extendsubstantially parallel to the rails 61. The movement of the arms 74 iscontrolled by means of a rod 79 which can be moved to and fro by meansof a cylinder 80.

At their protruding ends the arms 74 have been arranged in a hingedmanner to an elongated suction cup holder 75 which carries a greatnumber of vacuum suction cups 76 at its underside. These vacuum suctioncups are connected to a vacuum device 78 via the hollow internal spaceof the suction cup holder 75 and a flexible conduit 77. Suction by thevacuum device 78 can be turned on or off by means of valves 81.

For the purpose of moving the moulded door skins from the pressing area,the discharge carriage 70 is moved in between the moulds with the arms74 turned back, until it is level with the door skins 3. Next thecylinders 73 are activated by suitable control means as a result ofwhich the arm carriers 71 move upwards. Then the cylinders 80, on eitherside of the frame, are activated as a result of which the arms 74 areturned into their position illustrated in FIG. 11. By subsequentlylowering the cylinders 73 again the suction cups 76 make contact withthe end surfaces of the moulded door skins 3. Next the vacuum is createdso that the suction cups attach themselves firmly to the door skin 3.During the next phase the cylinders 73 are activated again for thepurpose of lifting the arm carriers 71 so that the door skin 3 is liftedoff the lower mould. The discharge carriage 70, with the door skinscarried by the suction cups, can then be moved out of the pressing areaoutside until it is positioned above the belt conveyor 82 arrangedthere.

Next the door skins 3 are lowered onto the belt conveyor 82 and thesuction cups are turned away after which the belt conveyor 82 is turnedon and the door skins can be moved away. In the mean time the supplycarriage can already place the next board in the press, where the nextpressing cycle can begin.

As has been mentioned before, the upper and lower mould of the preferredembodiment of the device illustrated consist of six separate sets ofmoulds, each for extruding one door skin. In the figures these six setsof moulds have each time been illustrated as being identical, but it isobviously possible to employ different sets of moulds in a suitablearrangement, depending on the required production.

In order to be able to change the production rapidly from door skins tobe made with a first series of mould sets to door skins to be made witha second series of mould sets the device according to the inventioncomprises preferably the rapid fastening system for mould plates. Thisrapid fastening system will be described below with reference to theFIGS. 10-15.

Each mould part is arranged separately in the press by means ofcylinders. Each upper mould part 87 and each lower mould part 86 hasbeen provided with a number of notches along its longitudinal end. Twoof these notches 90 are designed to engage the cylinders 88 with whichthe plate concerned is held to the press. In addition to these cylinders88 two auxiliary cylinders 92 have been arranged on either side to themovable press platen 59 for each set of mould parts 86,87. The headsthereof, to be described below, can engage in notches 93 in the lowermould part 86.

The mould changing device 85 works as follows.

Starting point is the closed position of the press as illustrated inFIG. 12 and in greater detail in FIG. 13. In between the mould partsmoulded door skins have been received, so that the mould parts cannotmake direct contact with one another so as not to damage them.

In order to be able to change the mould parts, the auxiliary cylinders92 are activated in such a way that the turning heads 94 thereof arefirst rotated a quarter turn and are next moved down into the notch 93of the lower mould part 86 by the auxiliary cylinder 92. Next theturning heads 94 are rotated back a quarter turn and the auxiliarycylinder 92 is activated in such a way that the turning head 94 ispulled upwards. When that happens the turning head 94 fits with itprotruding sections under the shoulder 95 of the notch 93 so that theyengage the lower mould parts in this manner.

Next the cylinders 88 are deactivated and its turning heads 89 rotated aquarter turn, so that they are released form the cooperating shoulders91 of the notches 90.

The suction rods of the cylinders 88 are then pulled in so that theturning heads 89 no longer engage the mould parts.

The situation which has been brought about in this way has beenillustrated in FIG. 14. The lower mould parts 86 are now pulled againstand retained together with the upper mould parts 87 against the movablepress platen 59 of the press 7 by the auxiliary cylinders 92.

Next the press is activated in such a way that the movable press platen59 moves upwards. The complete upper and lower moulds are moved alongand hang from the press platen 59.

The next phase has been illustrated in FIG. 15. In this figure it can beseen that the supply carriage 62 has entered the pressing area, wherebya carrier frame 97 has been mounted on the carriage 62. When thecarriage 62 together with the carrier frame 97 is positioned level withthe mould, the press 7 is activated in order to lower the press platen59 gradually until the lower mould parts 86 rest on the support beams 98of the carrier frame 97. Then the auxiliary cylinders 92 are activatedagain in such a way that they move the corresponding turning heads alittle downwards, turn them a quarter turn and move them upwards. Atthat moment the connection with the press platen 59 is broken and thepress is activated in order to move the press platen 59 upwards. At thatmoment the mould parts are supported by the carrier frame 97 and can bemoved outside with the carriage 62 out of the pressing area.

A hoisting mechanism not illustrated here can lift the carrier frame 97from the supply carriage 62 and replace it with another carrier frame 97with another set of mould parts which can be moved into the pressingarea of the press 7 again, after which the auxiliary cylinders 92 engageafter moving the press platen 59 downwards. The press platen 59 thenlifts the mould parts from the carrier frame 97 and this frame 97 isremoved together with the carriage 62 from the pressing area. The pressplaten 59 can then be moved down again until the lower mould parts arelying on the support of the press. After activating the cylinders 88concerned and deactivating the auxiliary cylinders 92 the press is readyfor use again.

1. Method of deforming a wood fibre board blank into a shaped product ina mould cavity in a press having at least an upper mould and lowermould, at least one of the upper mould and the lower mould movabletoward the other from a first open position for receiving the blank to asecond closed position defining the mould cavity, the method comprising:heating the blank to a thermo softening point such that the material ofthe blank is plastically deformable; providing the mould cavity in theclosed position with at least one constriction adapted to restrictlateral extrusion flow of the softened material of the blank, theconstriction located to prevent defects in the shaped product; heatingat least one of the upper mould and the lower mould; and pressing theblank in the mould cavity in a pressing cycle comprising at least oneperiod of gradual progressive deforming followed by at least one periodof rest while heating without opening the mould cavity.
 2. Method asclaimed in claim 1, wherein heating of the board comprises steamtreatment of the board.
 3. Method as claimed in claim 2, comprising ofheating the board in a closed space and, prior to heating, furtherreducing the pressure in the space and introducing the steam into thespace in a free flow.
 4. Method as claimed in claim 3, furthercomprising of heating at least the ceiling of the space to a highertemperature than the space.
 5. Method as claimed in claim 3, furthercomprising heating the walls of the space.
 6. Method as claimed in claim1, wherein pressing takes place in conjunction with the heating of themould parts or holders therefore applied in the pressing.
 7. Method asclaimed in claim 1, wherein the pressing comprises a pressing cycle withat least one decrease to an approximately pressureless state and asubsequent increase of the pressure on mould parts used during thepressing.
 8. Method as claimed in claim 1, wherein the pressingcomprises of rapid closing of mould parts used therein and relativelyslow build-up and decrease in the pressure.
 9. Method as claimed inclaim 1, further comprising pressing, together with the board, a coverlayer for covering the board subjected to the pressing.
 10. Method asclaimed in claim 1, further comprising of arranging a relief, during thepressing, in the visual surface of the board subjected to the pressing.11. Device for deforming a wood fibre board blank into a shaped productcomprising: a means for heating the blank to a thermo softening pointsuch that the material of the blank is plastically deformable; a presshaving at least an upper mould and a lower mould, at least one of theupper mould and lower mould movable toward the other from a first openposition for receiving the blank to a second closed position defining amould cavity; and at least one constriction in the mould cavity in theclosed position, the constriction adapted to restrict lateral extrusionflow of the softened material of the blank, the constriction located toprevent defects in the shaped product; wherein at least one of the uppermould and the lower mould is adapted to be heated and wherein theapparatus is adapted to press the blank in the mould apparatus isadapted to press the blank in the mould cavity in a pressing cyclecomprising at least one period of gradual progressive deforming followedby at lest one period of rest while heating without opening the mouldcavity.
 12. Device as claimed in claim 11, comprising heating means inat least a ceiling of a forming station operably associated with saidpress.
 13. Device as claimed in claim 11, further comprising heatingmeans in the interior of the mould apparatus.
 14. Device as claimed inclaim 13, wherein the heating means comprise guide channels forpre-heated oil.
 15. Device as claimed in claim 11, wherein the presscomprises rapid-action coupling means for engaging selected mould parts.16. Device as claimed in claim 11, wherein the mould parts aresub-divided into at least two mould part components to be energizedseparately of each other.
 17. Device as claimed in claim 11, furthercomprising transport means for transporting the boards from and to thepress.
 18. A method of manufacturing a hollow core door comprising thesteps of: providing a wood composite flat blank; moisturizing the flatblank; pre-heating at least a surface of the flat blank to a temperaturenot exceeding approximately 100° C.; positioning the flat blank in apress between first and second platens, at least one of the first andsecond platens being heated; closing the press on the flat blank andreforming the flat blank into a molded door skin including a pluralityof panels by applying a first pressure to the flat blank in the pressand thereafter applying a second higher pressure to the flat blank inthe press; affixing the molded door skin to a first side of a doorframe; and affixing a second door skin to an opposite second side of thedoor frame.
 19. Method as claimed in claim 18, wherein the step ofpre-heating the blank comprises the step of applying steam to the blank.20. Method as claimed in claim 19, wherein the pre-heating of the blankoccurs in a closed space and the steam is introduced into the closedspace in a free flow form.
 21. Method as claimed in claim 20, whereinthe closed space includes walls and a ceiling, the method furthercomprising the step of heating at least the ceiling of the space to ahigher temperature than the temperature of the remainder of the space.22. Method as claimed in claim 21, further comprising the step ofheating the walls of the space.
 23. Method as claimed in claim 19,wherein prior to the step of applying steam to the blank, the pressurein the space is reduced.
 24. Method as claimed in claim 19, includingthe additional step of heating the blank while the blank is reformed.25. Method as claimed in claim 18, wherein the step of reforming theflat blank comprises the steps of applying a first pressure to the flatblank in the press and reducing the pressure applied to the flat blankin the press to a level between said first pressure and atmosphericpressure.
 26. Method as claimed in claim 18, wherein the step ofreforming the flat blank comprises the steps of applying a firstpressure to the flat blank in the press and maintaining said firstpressure for a predetermined period of time.
 27. Method as claimed inclaim 18, wherein the step of closing the press on the flat blankcomprises the step of closing the press on the flat blank at a firstrate, and the step of reforming the flat blank comprises slowlyincreasing the pressure applied to the flat blank and then slowlydecreasing the pressure applied to the flat blank.
 28. Method as claimedin claim 18, further comprising the step of providing a covering layerto the flat blank after the pre-heating step.
 29. Method as claimed inclaim 18, further comprising the step of developing a relief on thesurface of the flat blank during the reforming step.
 30. Method asclaimed in claim 18, including the step of holding the temperature ofthe platens in a pre-selected range during the reforming step. 31.Method as claimed in claim 18, further comprising the step ofmaintaining a geometrically uniform gap between said first and secondplatens during the reforming step.
 32. Method as claimed in claim 18,further comprising the step of reforming the blank into a plurality ofmolded door skins.
 33. Method as claimed in claim 32, further comprisingthe step of forming a pinch between adjacent molded door skins tofacilitate the separation of the adjacent door skins from one another.34. Method as claimed in claim 18, further comprising the step ofembossing a texture on the molded door skins during the reforming step.35. Method as claimed in claim 18, further comprising the step ofproviding material which includes a thermosetting resin to thepre-heated blank.
 36. Device for reforming a wood fiber board blank intoa finished product having areas of considerable difference in heightrelative to the original thickness of the wood fiber board blank,comprising: a first station with a blank heater and a blank moisturizer;a second station for pressing a blank to a desired form, said secondstation comprising: first and second opposing platens each having a moldattached thereto; and a controller for controlling the opening andclosing of the platens and the amount of pressure applied to a blankpositioned between the platens; said controller gradually increasing thepressure on a blank to a predetermined pressure, maintaining thepredetermined pressure at a predetermined level for a predeterminedperiod of time and gradually reducing the pressure to approximately zeroduring a pressing cycle.
 37. Device as claimed in claim 36, furthercomprising heating means in the interior of the platens or molds. 38.Device as claimed in claim 36, including guide channels in at least oneof said first and second platens for carrying heated oil.
 39. Device asclaimed in claim 36 wherein the second station further comprises anattachment mechanism for connecting a mold to one of said first andsecond platens.
 40. Device as claimed in claims 36, further comprising aconveyor for conveying blanks to the first station, from the firststation to the second station and from the second station.
 41. Device asclaimed in claim 36 wherein said first and second molds have projectionsfor reducing displacement of wood fiber material in a wood fiber boardat locations between the molds where the blanks are subjected to themost severe shear loads during a pressing operation.
 42. Device asclaimed in claim 36 further comprising automated means for switching themolds on the device.
 43. A door skin, comprising: a medium density fiberboard flat blank that has been molded using heat, pressure and degassinginto a three-dimensional blank, said fiber board blank being degassedwhile being molded into said three dimensional blank, said threedimensional blank having a first portion with a first preselectedthickness and a second portion with a second preselected thickness lessthan said first preselected thickness.
 44. A hollow core doorcomprising: a door frame; a first door skin comprising a medium densityfiberboard flat blank reformed into a three-dimensional blank having aplurality of panels and a second door skin attached to said door frameso as to define a hollow core area therebetween; said reformed door skinhaving a first molded portion with a first preselected thickness and asecond molded portion with a second preselected thickness less than saidfirst preselected thickness.
 45. A press for molding door skins,comprising: first and second heatable platens; a plurality of openingsin the side of at least one of said first and second platens fordegassing; and an actuator for moving said first platen toward and awayfrom the said second platen, thereby opening and closing the press.